I used to think it was some sort of alien creature, too, when I wasn't very familiar with the DOOM mythos. However, it does kind of look like the face of the clay model of the Arch-Vile, and if they made one DOOM 1 texture into a DOOM II monster (Icon of Sin), it stands to reason they might have with another.

Looking at the two images side-by-side in Technician's post, the "curvy side-bones" are clearly visible in the actual Arch-Vile sprite -- MARBFAC2 simply can't be anything else, although for all we know id could've made the monster similar after-the-fact. ;)

Worst said:
maybe it'll look more like a vile if you remove the curvy bones next to the jaw

To me it looks like the in-game arch-vile sprites have those same tubular structures; the first image in Technician's post shows them, though the source model lacks them. The model does better showcase the teeth than the sprites do.

Regardless of whether Adrian had the arch-vile design concept in his head when he was making the MARBFAC2 texture, the source model was of course made by Gregor Punchatz; this might explain why MARBFAC2's features don't align with the arch-vile model as much as MARBFAC3 does with the baron model and sprites.

Extremely low resolutions will do that. The sprite head is like 13 pixels wide, whereas the MARBFACE version is probably closer to about 80. You can see where the eye area is; the colour gets much darker. It's definitely the same face